As is described in the U.S. Pat. No. 4,060,810, a microstrip antenna is a printed circuit device in which the radiating element is typically a rectangular patch of metal etched on one side of a dual-clad circuit board, with the size of the element being dependent upon the resonant frequencies desired and upon the dielectric constant of the circuit board material. It was there noted that in those instances where it was desired to combine a microstrip antenna operating at the L-band of frequencies with a horn radiator operating at the X-band of frequencies -- for a parabolic dish reflector, for example --, the resultant construction could lead to a reduced efficiency of operation because of aperture blockage, unless the reflector were increased in size. This, however, made the combination fairly cumbersome and increased its manufacturing costs.
As was described, the microstrip antenna design of that application followed from a finding that the resonant frequency of a given size radiator decreased if a central portion of the etched metal element were removed. With its additional described finding that the size of the radiator could be reduced and yet still operate at the same resonant frequency, simplifications in microstrip antenna designs could be made -- including the fabrication of a dual frequency arrangement in which an antenna operating at X-band was printed on the same dual-clad circuit board as an antenna operating at L-band, when the X-band radiator was positioned in the portion of the etched metal element removed from the L-band radiator. By thus being able to reduce the size of the microstrip antenna for a given frequency, it was noted that the overall antenna feed could be reduced in dimension, so as to enable the dish reflector, for example, to be similarly decreased in size, while maintaining the same degree of aperture blockage. As was additionally noted, the techniques described therein were applicable not only to dual-frequency arrangements, but to multiple frequency capability arrangements, as well.